Fluidity of Cement Paste with Air-Cooled Blast Furnace Slag

Air-cooled slag showed grindability approximately twice as good as that of water-cooled slag. While the studied water-cooled slag was composed of glass as constituent mineral, the air-cooled slag was mainly composed of melilite. It is assumed that the sulfur in air-cooled slag is mainly in the form of CaS, which is oxidized into CaS2O3 when in contact with air. CaS2O3, then, is released mainly as S(2)O(3)(2-)ion when in contact with water. However, the sulfur in water-cooled slag functioned as a constituent of the glass structure, so the S(2)O(3)(2-)ion was not released even when in contact with water. When no chemical admixture was added, the blended cement of aircooled slag showed higher fluidity and retention effect than those of the blended cement of the water-cooled slag. It seems that these discrepancies are caused by the initial hydration inhibition effect of cement by the S(2)O(3)(2-)ion of air-cooled slag. When a superplasticizer is added, the air-cooled slag used more superplasticizer than did the blast furnace slag for the same flow because the air-cooled slag had higher specific surface area due to the presence of micro-pores. Meanwhile, the blended cement of the air-cooled slag showed a greater fluidity retention effect than that of the blended cement of the water-cooled slag. This may be a combined effect of the increased use of superplasticizer and the presence of released S(2)O(3)(2-)ion; however, further, more detailed studies will need to be conducted.